The move comes ahead of next year's Mumbai civic elections, where Congress would be seeking to dislodge the incumbent Shiv Sena-BJP combine.
In a statement to media this evening, 61-year-old Kamat said, "Dear friends, over the last more than 44 years I have worked with most of you and served the Congress. For several months now I have felt I need to take a backseat to enable others to get the opportunity."
"I met the honourable Congress president about 10 days ago and expressed a desire to resign. Subsequently I sent letters to both Soniaji and Rahulji that I would like to exit.